Pump



w. F. sTREHLow ET AL 2,611,319

Sept. 23, 1952 PUMP Filed May 12I 1948 5 Sheets-Sheet 1 Patented Sept. 23, 195i? PUMP Walter F. Strehlow, Wauwatosa, and Igor Kamlukin,

Milwaukee, Wis., assignors to Allis- Chalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application May 12, 1948, Serial No. 26,516

25 Claims.

This invention relates generally to hydraulic control apparatus and is more particularly directed toward apparatus for controlling a hydraulic pump so Vas to afford a positive variable discharge of pressure maintaining uid.

It is an object of the present invention to provide a hydraulic pump having parts, including a flow control valve and a pressure relief means, constructed and combined in an improved manner for efliciently decreasing the quantity of pressure maintaining fluid in response to attainment of a predetermined fluid pressure.

Another object of the present invention is to provide a hydraulic pump with control and pressure relief means combined for coaction in a novel and improved manner affording a reduction of hydraulic pressure on the pumpupon attainment of a predetermined pressure head and thereafter operating to efficiently maintain areduced pressure head. s

It is also an object of this invention to provide a pump unit, adapted for operating a hydraulic motor, with a control valve and pressure relief means constructed and combined for coaction in an improved manner affording a manual control for selectively varying the quantity of pressure maintaining iiuid discharged by the pump, as desired, and also affording means, independent of the manual setting of said control valve,v for eiiciently decreasing theV discharge of pressure maintaining fluid whenever the fluid foroperating the motor attains a predetermined pressure.

Still another object'of the present invention is to provide a pump unit with a pressurerelief and control means combined for coaction in an improved manner operative to eiciently maintain a desired pressure head with a minimum discharge of pressure maintaining fluid.

An additional object of this invention is to provide a multiple plunger pump, adapted for use with a hydraulic ram, with parts including external control means combined for coaction in an improved, manner such that a single movement of acontrol lever results in the ram piston moving to and being hydraulically locked one ofits limiting positions and such that a pressurehead suicient to retain the ram piston locked in its 'l 'as the disclosure progresses and particularly points out the various advantages and other features considered of special-importance. And accordingly, the present invention maybe considered as comprising the various constructions, combinations, and/or subcombinations asishereinafter more fully set forth in thedetailed description and appended claims, reference being had to the accompanying drawings, in which:

Fig. 1 is a partial plan view ofapparatus embodying the invention with parts broken away and other parts indicated schematically;

Fig. 2 is a sectional'view taken on line II-II of Fig. l;

Fig. 3 is a sectional view taken on line III-III of Fig. 2;

Fig. 4 is a sectional view taken on line IV-IV of Fig. 2; Y .y f y Fig. 5 is a sectional view taken on line `V---V of Fig. 2;

Fig. 6 is another sectional View taken on line VI-VI of Fig. 4; Y

Fig. 7 is a schematic showing, partly in section, of the apparatus Vembodying the invention;

Fig. 8 is a View of the valve structure shown in Fig. 'l indicating a different position thereof; and

Fig. 9 is a View somewhat similar to Fig. 8 illustrating still another position of the control valve.

Referring to Fig. l it will be seen that the illustrated embodiment of Athe present invention comprises a hollow lubricant confining casing I operatively enclosing a rotatingshaft 2 driven from any suitable power source (not shown) andprovided with cam portions 3, A side wall ofhollow structure I is provided with an opening 4 therethrough which kexposes the cam portions 3` on shaft 2. And a hydraulic pump and control unit comprising a housing l is detachably secured to the side of hollow structure I (as by .bolts 8) in covering relation with respectto the opening 4 therethrough. The side of housingl'l opposing opening 4 in hollow casing I is .provided with marginal surfaces 9 for sealingly engaging the side wall surfaces of casing I which bound opening 4. A hydraulic motor I I, in this case a single acting ram unit, is operatively connected with the pump and control unit housing-'I #by a conduit I2 for the ow of lubricant to and from A'the ram. Ram piston I3 isoperatively `connected with one arm of a bellcrank lever I4: having a weight I6 or other device attached toits other arm for actuation by the ram unit. As shown, the ram is in its retracted position and upon admission of pressure fluid thereto piston'element I3 movesI to the right and raisesweight lr6.

Referring also to Figs. 2 to 6, inclusive, it will be apparent thatthe side of pump Vhousing? enclosing the opening in hollow structure I is provided with four inwardly extending parallel cylindrical chambers I1, I8, I9 and 23, chambers I1, IB and I9 being of equal diametei` and chamber having a materially reduced diameter. A compression spring 22 (see Fig. 4) is positioned within each chamber at the inner end thereof and each chamber includes a pump plunger 23 having a reduced inner end portion 24 disposed in guiding relation within the associated compression spring 22. The side of housing 1 adjacent hollow casing I is also provided with outwardly extending projections 25 having aligned holes therethrough receiving and xedly mounting a shaft or rod part 21 disposed at a right angle with respect to the axes of pump plungers 23 and generally parallel to a plane therethrough. And a plurality of cam followers 2S, one for each pump, are pivotally supported on shaft part 21 for swinging movement relative thereto and relative to each other, the lower end portions of these followers being disposed between the outer ends of pump plungers 23 and the opposed cam portions 3 on shaft 2 thereby establishing an operative connection between power driven shaft 2 and pump unit 6. (See Fig. l.)

Pump housing 1 is provided with an intake manifold passage 29 severally communicating with pump chambers I1 to 20 through intake passages 3| and communicating with the lubricant in hollow structure I through a main intake passage 32 terminating in the adjacent side of housing 'l below the pump plungers therein. Passage 32 includes an extending conduit portion 33 (see Fig. 4) projecting outward therefrom through the opening 4 and downward into the fluid conned in hollow casing I. Housing 1 is also provided with a cylindrical valve chamber 34 which extends therethrough in spaced overlying relation with respect to pump cylinders I1 to 23 and in parallel right angle relation thereto. A plurality of passages 36, one for each pump, severally connect the inner or discharge ends of the pump cylinders with longitudinally spaced portions of cylindrical valve chamber 34. In addition, housing 1 includes a horizontal bore 31 which is disposed above valve chamber 34 in generally parallel relation thereto and which is connected therewith through a group of passages 38 corresponding in number to pump discharge passages 36. And in this connection it should be noted that passages 38 communicate with valve chamber 34 in diametrically opposed relation to passages 36. Each passage 33 is provided with a spring biased ballcheck valve controlling the flow of fluid therethrough and into bore 31. This bore, which may be considered a manifold space, communicates at its right hand end (note Figs. l and 2) with an outlet passage 4I for working fluid which terminates in an upwardly extending pipe connection 42 provided with a suitable connector 43 for coupling a ram hose or the like thereto. Communication between outlet passage 4I and manifold space 31 is controlled by a spring biased ballcheck valve 44 preventing a back flow of fluid from passage 4I into the manifold space. In addition it should be noted that this discharge fluid passage 4I has a branch portion 45 on the discharge side of check valve 44 placing same in communication with the right hand end of cylindrical valve chamber 34.

. Housing 1 is also provided with a main fluid return passage means comprising a horizontal bore opening 46 through the side surface of the housing closing the opening in hollow casing I at a point somewhat below and to one side of intake conduit 33 (Fig. 6). The inner end of return passage bore 43 communicates with a bore 41 at right angles thereto (Fig. 5) which extends nearly through the pump housing in generally parallel relation to and `below valve chamber 34. This bore 41 is also disposed` below pump chambers I1 to 2B and a plurality of passages 43 corresponding in number to pump discharge passages 35 place this bore in communication with longitudinally spaced portions of cylindrical valve chamber 34, these passages 48 being disposed adjacent the pump cylinder chambers and the passages 35 severally connecting the discharge side of the pumps with longitudinally spaced portions of cylindrical y valve chamber 34 as previously described. Another passage 49 places main return passage bore 41 in communication with a right end portion of valve chamber 34 in longitudinally offset diametrically opposed relation with respect to the branch portion 45 .of outlet passage 4I.

In addition, housing 1 is provided with a cylindrical unloading chamber 5I extending therethrough in laterally spaced parallel relation with respect to cylindrical valve chamber 34 and on a horizontal level therewith. The left hand end of manifold bore 31 communicates with the adjacent end of unloading chamber 5I by means of a passage 52 (Fig. 6) and an intermediate portion of this unloading chamber communicates with a horizontal discharge passage A53 (Figs. 3 and 4) opening through the side surface of the pump housing above the pump chambers.

The left end portion 50 of unloading chamber 5I is somewhat enlarged to provide an internal shoulder 54 against which is positioned a disk type spring seat 56 having an opening 51 therethrough. The opposite or left hand end of chamber portion 5I) is closed by a cylindrical plug element 58 having an inner end portion 59 of reduced diameter projecting axially toward spring seat 56 in spaced relation with respect to the surrounding wall of chamber 5I. The left hand end of plug member 58 is provided with a circumferential external groove 6I communicating with passage 52 leading thereto from manifold space 31. A transverse bore 62 connects diametrically opposed portions of groove 6I with a central bore 63 which extends inward from transverse bore 62 and coaxially through the reduced portion 59 of plug member 58. Central bore 63 is enlarged from a point adjacent transverse bore 62 to the discharge side thereof to provide a seat for a ball valve 64 and to receive cylindrical valve element B6. A cylindrical spring seat element 61 slidably surrounds the reduced end portion 59 of plug member 58 and is provided at its open end with a peripheral flange 68 slidably engaging the internal surface of unloading chamber portion 5U, this flange also affording a seat for a compression spring 69 disposed between same and disk seat 56. The inner end of element 51 is provided with an internal recess forming a cylindrical seat 10 receiving the inner end of cylindrical valve element 66 which, through the action of spring 69, acts to hold this valve element and ball valve 64 positioned as shown in Fig. 3, that is, with the'ball valve firmly engaged with its seat thereby preventing a flow of fluid therepast from manifold 31. And when thus positioned, it will be noted that the flanged end of spring seat element 61 is spaced from the opposed inwardly facing shoulder presented by plug member 58. The reduced portion 59 of plug member 58 is provided with a transverse bore 1| therethrough and is further reduced from its junction with the'main portion of the plug member 58 inward to point beyond transverse bore 1| so as to provide an annular relief passage 12 which communicates with the spring housing portion of chamber 50 through one or more axial slots in the peripheral edge portion of flange 98. Cylindrical valve element -66 is also provided with an axial bore 13 extending from the ball valve end thereof approximately to its midpoint where it communicates with a circumferential groove 14 adapted to place the space between the end of valve element 66 and the seat for ball yvalve $4 in communication with the transverse bore 1| in plug member portion 59, thus providing a relief passage means forrthe space surrounding ball valve 64 when seated as shown in Fig. 3. Also, the inner end portion of cylindrical spring .seat element 61 is provided with transverse bore 18 therethrough for relief of liquid tending to accumulate between same and the inner end of plug member reduced portion 59.

The left hand end of unloading chamber 5| and of cylindrical valve chamber 34 are closed by a cover plate 11 secured in end abutting relation to housing 1 by means of cap screws 18 or the like. The right hand end of unloading chamber 5| mounts a cylindrical spring seat 19 and is closed, as is also the corresponding end of valve chamber 34, by means of a'cover plate 80 xedly secured thereto by one or more cap screws 85. A pressure responsive piston 8| is mounted in unloading chamber I5| in down stream relation with respect to spring seat disk 58 and is detachably connected with a vmovement transmitting rod 82 which extends coaxially through cylindrical spring seat 19 and through an aligned and somewhat enlarged opening 93 in cover plate 80. The outer or exposed end of control rod 82 is xedly connected with and carries a stub shaft 83 which projects at a right angle therefrom in the direction of valve chamber 34 and in generally parallel relation to cover plate 80. A compression spring 84 is interposed between seat 19 and the opposed end of piston 8| to fluid return passage 53. It will be noted that o the right hand end of unloading chamber 5| is provided with another uid return passage 86 (Fig. 3) opening through the side face of the housing enclosing opening 4, this additional passage functioning to return any liquid tending to become trapped between piston 8| and cylindrical spring seat 19.

Referring again to Fig. 2 it will be seen that a cylindrical liner comprising axially separable sections 88 to 92 is disposedin cylindrical valve chamber 34 with innermost section 92; that is, the section adjacent the right hand end of chamber 34,` abutting cover plate 80. The opposite endsection 88, that is, the section at the left hand end 'of chamber 34 is held in position by end abutting engagement with cover plate 11. Cylindrical sections 88 to 92 are provided with circumferential external grooves 94 placing pump discharge passages 30 in communication with check valve control passages 38. In addition each sectionis provided with transverse bores 98 (see also Fig. 3) placing the interior thereof in communication with diametrically opposed pairs of passages 36 and 38. Furthermore the end abutting portions of cylindrical sections have parts thereof cut away and shaped to' afford circumferensages 48 placing same in communication with thernain iiuid returnpassage 41. In addition, the innermost cylindrical section 92 is provided with two circumferential external grooves, the innermost groove 93 communicating with ram outlet passage 4| and having a'transverse bore 99 therethrough placing diametrically opposed portions of grooves 98 in communication with the interior of section 92, and a second groove |00 `communicating with a passage 49 which in turn communicates with the right hand end of main fluid return passage 41. Groove |00 also communicates with the interior of liner section 92 through diametrically opposed transverse bores A cylindrical control valve |02 is positioned in the generally cylindrical chamber formed by the end 'abutting liner sections 88-92 and preferably this valve is formed by a series of separable cylindrical elements, |03- |05 inclusive, disposed in end abutting relation, the end abutting portions of these cylindrical valve elements being reduced to form annular spaces between same and the surrounding internal surfaces of the liner sections. In this connection it should be noted that the right hand or innermost'valve element |08 comprises an intermediate reduced portion |01 uniting enlarged cylindrical portions |08 and |09 which in turn terminate in reduced oppositely projecting end portions, the inner one of which abuts the reduced portion on adjacent element |05 and the other of which projects through a coaxial-opening in cover plate 80. The valve elements are held in end abutting relation for movement as a unit by means of a compression spring ||2 seated on valve element |03 in surrounding relation tO the reduced outer end portion thereof with its opposite end abutting the inner surface of cover plate 11. Movement of the valve element to the left as viewed in Fig. 2 may be adjustably limited through the medium of an inwardly projecting part ||3 carried by cover member 11, this part having an internally threaded bore ||4 extending therethrough in which is adjustably mounted a screw threaded element ||6 having a reduced end portion |1 disposed in coaxial abutting relation with respect to a similar projection on the adjacent valve element |03. The outer exposed end of element ||6 is provided with a knurled adjusting knob I8.

Referring more particularly to Figs. 3 and 6 it will be noted that the shaft portion 83 carried by control rod 82 operatively mounts a roller ||9 positioned in opposed engaged relation with respect to the reduced end portion of the innermost valve element |06 which extends through cover plate 80. Shaft 83 also has connected therewith the upper end of a lever |2| having an intermediate portion thereof pivotally connected with a link |22 which in turn is pivotally connected with an arm |23 fixed to an inner end portion of a shaft |24 rotatably supported in a bearing structure |29 carried'by control linkage housing |21. This housing is `detachably secured in abutting sealed relation against cover plate by means of suitable cap screws or the like |28. And in this connection it should be noted that cover plate 80 is provided with suitable openings |29 and |3| which are aligned with and place main inlet passage bore 29 and main return passage bore 41, respectively, in communication with the interior of the linkage housing |21. Consequently this housing contains oil at a level conforming with that in hollow structure The outer end of shaft |24 has a lever arm |32 fixed thereto which in turn may be connected through a link or other means (not shown) with a suitable manually actuable control lever |33 as indicated in Fig. 1. The bottom portion of housing |21 is provided with an adjustable stop means |34 positioned in opposed engageable relation in respect to the lower edge of lever |2|. Spring 84 in unloading chamber 5| is relatively strong as compared with the spring ||2 acting on control valve |02 and consequently piston 8|, control rod 82 and valve |02 tend to assume the position shown in Figs. 2 and 3. However, it should be noted that the manual control lever |33 may be moved so as to shift the fulcrum for lever |2 l, that is the fulcrum afforded by the connection oflinl; |22 to an intermediate portion of lever` |2|, and thereby move the rod 02 and piston 8| toward the right as viewed in Fig. 4 which in turn compresses spring 84. As a result of such movement, spring ||2 urges control valve |02 toward the right (note Fig. 3) and acts to maintain the reduced righthand end of this valve in engagement with roller ||9. Movement of the valve |02 in the direction just described, that is, toward the right is limited by engagement of the enlarged portion |09 of valve element |09 with cover plate 80.

When operating with the parts positioned as shown in Figs. 2 and 3, it will be noted that the enlarged cylindrical portions of the valve elements IGS-|06 inclusive, close transverse bores 96 and that, therefore, the pumps are severally connected with manifold space 31 through passages 35, external grooves 94, and through check valve controlled passages 38. The liquid entering manifold space 31, assuming all liquid has been drained from the ram ows therefrom through check valve control passage 4| and quickly attains a pressure suicient to rapidly effect a weight lifting power stroke or expansion of the ram unit. When this occurs the pressure of the liquid in manifold space 31 continues to increase until the pressure attained is sufficient to unseat pressure relief ball valve 64 whereupon the ycheck valve assembly comprising ball lValve 64 and cylindrical valve element 66 moves toward the right compressing spring 69 until a valve element 66 opens transverse pressure relief bore 1|. When this occurs, pressure fluid ows therethrough into annular space 12, then through the axial passages in the periphery of flange portion 68 of spring seat element 61, then into the spring housing chamber from which it flows through the opening 51 in disk valve seat 56 and then into the space between this seat and the head of piston 8|. This pressure fluid then acts on piston 8| and moves same toward the right thereby opening relierc passage 53 which is in communication with the source of oil in hollow structure and in linkage housing |21. This movement of piston Si results in a movement of control rod 82 toward the right sufficient to bring the lower end of lever |2| into engagement with the side of cover plate 80 which engagement limits the movement of the piston 8| and control rod 82 in this direction. As a result spring ||2 causes control valve |02 to move toward the right in following engaged relation to roller part ||9 and to the position indicated in Fig. 7. In this position,.the enlarged .b'ore controlling portions of valve elements |03, |04 and |05, place transverse bores 96 in the associated liners in communication with return passages 48 thereby severally connecting the discharge sides of pumps |1, |8 and |9 in communication with the main return passage bore 41. However, it should be noted that the enlarged portions |08 and |09 of valve element |96 remains in closed relation with respect to transverse bores 96 and 99, respectively, and therefore pump 20 continues to deliver iluid through circumferential groove ||0 and into manifold space 31 through the associated check valve control passage 38.

It should be noted that the end area of cylindrical relief valve element 66 is considerably greater than the area of the passage controlled by ball valve 64 and that consequently it requires a relatively high pressure to effect an initial opening movement of these two valves. However, once an opening relation is established, the increase in effective area afforded by cylin- .drical relief valve element 66 operates to maintain the relief passage means open under a considerably reduced pressure head. Therefore, in the position just described, that is, the unloading position of main control valve |02, three plungers |1, i9 and I9 are delivering fluid to the return passage means 41 whereas only one plunger 20 is delivering fluid to the manifold space 31 and this iiuid, assuming there is no appreciable leakage from the ram circuit, returns to the source through the relief means comprising passage 52, bores 62 and 63 in plug element 58, relief valve elements 64 and 66, transverse bore 1| in plug element reduced portion 59, passages 12 and 15, the opening 51 through disk seat 56, and passage 53. In this connection it may be well to note at this time that although the enlarged cylindrical flow controlling portions of valve |92 are of substantially equal axial length,

the reduced portions are of different axial lengths and in addition the axial spacing of the circumferential grooves 94, 91, |00 and 9 8 and of the transverse bores or passages 95, 96, |0| and 99 connected therewith vary somewhat as to their axial spacing so as to afford the above mentioned regulation in response to an unloading movement of the control valve.

In the absence of excessive leakage, more particularly leakage through the flexible hose I2 and the connections between such hose and the ram cylinder and pump housing 1, the main control valve will remain in its unloading position until the fulcrum of lever |2| is shifted by actuation of manual control lever |33. Under these conditions the hydraulic ram unit will remain in its extended weight lifting position but if for any reason the pressure in manifold space 31 should decrease below that necessary to hold ball valve 64 and cylindrical relief valve 65 in their passage opening positions (note Fig. 7), these valves will close the relief passage means 52 and as the liquid drains from the space ahead of piston 9|, the spring 84 will move the piston and control rod 82 to the left thus repositioning the main control valve |02 to conneet all pumps with the check valve control passages 38 leading to manifold space 31, this initial position of the main control valve being determined, as previously indicated, by the position of manual control lever |33.

'Howeveig if with the control valve |02 in either its full lift or unloading positions previously described it becomes desirable to lower the weight, all that has to be done is Vto'move manual control the main control valve |02 to the right until the enlarged end portion |09 thereof engages cover plate 80 as shown in Fig. 8. K This position, termed the lowering position of the valve, places the discharge sides of all pumps and the ram relief passage means 45 and 99 in communication with return passages 48 and 49 which in turn are in continuous' communication with the main-return passage means 4l. Under these conditions `liquid rapidly drains from the ram circuit, the ram piston moving to its retracted position through gravity action of the weight or other means actuated thereby. In other Words, if the weight were to be considered as representing an. agricultural implement or other load, movement of the valve |02 to its lowering position rapidly drops the implement onto the ground. If, however, it is desired to gradually lower'the weight or implement onto the-ground, this can be readily accomplished'simply by moving the main control valve |02 so as tojust barely open the passage means 99 placing the ram relief passage Y|15 in communication with the return passage means 49 and lll. And if in this connection it should be desired to place all pumpsv in communication with the return passage means 4l through passages 48 and yet retain the ram in its extended valve |02 closes thetransverse bore 99v placingl the ramy relief passage. in communication with the return passage means 49 and 4l. n

It should also be obvious that in addition to the various positions of the main control valve |02 hereinbefore described, the Valve may be also positioned by a manual shifting of the fulcrum for lever |2| so .as to, if. desired, effect a ram expanding action by connecting the discharge sides of two or more pumps with the check valve control passages 38 connecting same with manifold space 31. And Whileit is normally intended that the enlarged-cylindrical portions of the main control valve will be positioned so as to either open or close the radially extending transverse bores or passages placing the circumferential external grooves in communication with the interior of the valve chamber formed by the liner sections, it should be obvious that the valve elements may be positioned so as to only par-` tiallyv open one o1" more transverse passages. Furthermora'it should be apparent that While the particular arrangement of the passages and valveL elements herein shown for purposes of illustration constitutes a preferred embodiment of the present invention, other arrangements can-be readily. made as desired simply by changing the actual spacing of the control passages, circumferential grooves and/or the axial length of the enlarged passage controlling Vportions of the valve elements. V 1 l Referring again to Figs. 2, 7, 8, and 9, it will be apparent that the positionrof vvalve |02vdetermines whether theweight, implement or device connected with the ram` unit is to be raised, lowered` or held in a selected positionand, if the weight is being either raised or lowered, the rate of movement thereof. `In addition, it should be apparent that irrespective of the rate of lift, as soon as the pressure head on the pump' attains a predetermined value, therclf PSSagS means is immediately openedV through thecoaction of ball valve 64, cylindrical valve element 66, and piston 8|..A Furthermore, if the lift positionV of valve |02 is such that more than one plunger is delivering fluid to manifold space 3T, opening of the relief passage means results in an immediate movement of this valve to. its un- `loaded position shown in Fig. '7. yIn any case,

once the relief passage means is initially opened l in response to attainment of apressure. sufllf.

cient to unseat ball valve 64, it is held open by the then dominating action of cylindrical valve element 66 thereby Feffecting a material reduction in pressure head, as previously described.

In the operation of hydraulic motors, and more pressure is required to retain the load in theY position to which it has been shifted. For example the operation of a ram system such as herein disclosed, particularly'if, applied to, various..

types ofagricultural implements,l may require a power stroke pressure of as much or morethan 3500 pounds per square inch and a load retaining pressure of only 1200 'pounds per square inch.v In addition, if it were possible to maintain perfect seals, particular reference being had to the seating of valves 39 and i4 and the sealing action of the enlarged portion |09 of main valve section |06, operation of the pump means could be `dis,VV j

continued providing ram operation is infrequent.A

Usually, however, the ram is frequently operated` and its operation is nearly, continuous when apxplied as a draftregulatingdevice. Consequently,

the feature of Aeffecting a reduction in pressure head as previously pointed out is important in.,`

that it not only reduces pump load and heating, both of which are detrimental to pump lifebut it also eiciently compensates for leakage and conditions the system for an immediate response to load requirements.

It should also be apparent that the unloading of the pump be done quickly and autorriatically.v

whenever a reduction in pressure .head is feasible in order to minimize both operatingy and main-` tenanee costs. This automatic rapid unloading of the pump is readily achieved by apparatusY embodying the invention and is an important feature for the reasons just stated and for the further reason that it eliminates the possibility.

of damage which might result from failure -of an operator to quickly effect the necessary regulation. Still `ranother feature of importance` Thus fary the valves 39 and 44 have been con-,yA

sidered as spring biased check valves and nomention has been made as to the. degree of biasingA` action afforded by the springs associated therewith.v However, it should be apparent that the pressuremaintaining action afforded by these valves may be varied as desired simply by the Consequently, this.

selection of suitable springs. For example, the strength of the spring associated with valve 44 may be such that this valve actually controls the discharge of working fluid from manifold space 31 or merely prevents a return flow of liquid into manifold space 31 in the event the pressure therein should become less than the pressure in passage 4|. And in applying apparatus embodying the invention to the control of a ram unit as herein disclosed, the valve 44 could be omitted without materially affecting operation, since the primary function of this valve is to prevent a pressure relieving back-flow of liquid from the ram into manifold space 31. Consequently, it should be obvious that although certain advantages are afforded by the use of back-flow preventing valves in the working iluid passage means connected with a ram unit or like device, the invention in its broad aspects is applicable t any hydraulic apparatus utilizing a pressure maintaining pump and a valve means selectively positionable to-vary the volume of pressure maintaining fluid discharged by the pump.

As to the advantages afforded by the inclusion of check valves 39 and All, it should be apparent that when the pump unit is applied to a draft regulating device valve i4 prevents the relief mechanism .from responding to pressure surges or impulses transmitted to the system Whenever the ram voperated by the pump unit is subjected to a shock load. And, in the event that valve 44 sticks in a passage opening position, valves 39 provide protection for plungers 23 and parts associated therewith by preventing the back pressure created by action of the shock load on the system from reaching the plunger chambers. Furthermore, should the pump operating means stop for any reason .while control valve |02 is in its lift or unloaded position ball valve 44 will 'seat itself and the fluid in the ram and passage 4| will be locked therein preventing the weight or implement being lifted by the ram from dropping suddenly and causing possible damage. Y And, as previously mentioned, when valve |02 is in hold position (Fig. 9) with Vno pumps delivering to space 31 valves 39 prevent any leakage past valve '4d from being transmitted back through passage 38 to the plunger chambers. In the last mentioned case, if valves 39 are biased suillciently they will also serve to keep iluid discharged from the pumps from entering manifold 31 instead of flowing back to the source by Way of grooves 91, passages 95, and return passage means 6.8. Also, when less than all of the pumps are used for lifting, valves 39 are necessary to prevent a return flow of fluid from. manifold 31 through those passages 3B which are in communication with return passages 48 through the interior of the valve chamber.

It will also be noted that the previously mentioned unloading feature is of additional advantage in the event the manual control is in lift position and the ram is subjected to an excessive load. In such event the pump continues to attempt to lift the load until a predetermined maximum (unloading) pressure is built up in manifold 31 at Which instant the unloading and relief mechanism in chamber functions, as previously described, to relieve manifold 31 of excess pressure fluid and also to reduce the number of plungers 23 delivering to space 31. When the excess load ceases to exist the pressure in paspressure in space 31 and valve 44 opens to thereby reduce the pressure in space 31 and permit the ball valve and piston assembly in unloading chamber 5| to reseat itself. The return of the unloading mechanism to a passage closing position causes control valve |02 to move back to a full lift position and iluid is once more directed to the ram. Thus, there is provided a relief means which reduces the number of plungers delivering to the manifold space as long as the excess load exists and then automatically cuts the plungers baci; into communication with the manifold when the excess load disappears. This feature is of considerable importance in reducing the wear on the pump structure which otherwise might be considerable, particularly when relatively high pressure fluid is being used in the system.

And although the invention is illustrated as applied to afmultiple plunger pump-ram combination, it is to be understood that certain of the objects can be accomplished either with or Without the inclusion of a ram unit or other form of hydraulic motor and that it is not intended to limit the invention to the exact constructions and combinations herein shown and described as certain features thereof are of more general application and as various modifications Within the scope of the appended claims may occur to persons skilled in the art.

It is claimed and desired to secure by Letters Patent:

l. In a hydraulic apparatus including a pump means, means defining.v a valve chamber in continuous communication with said pump means for receiving pressure fluid therefrom, a fluid return passage means communicating with said valve chamber, and a Working fluid passage means communicating with said valve chamber and with said return passage means through inlet and relief valves respectively of a nature operating to maintain the iluid confined therein at a predetermined working pressure, and including a control valve in said chamber positionable to selectively connect said pump means with either said Working fluid passage means or Said return passage means, or with both, the combination of an unloading control comprising a part responsively associated with said relief Valve and being operatively connected with said control valve so as to move the latter to a position wherein less fluid is delivered to said confining space in response to a pressure relieving actuation of said relief valve.

2. In a hydraulic apparatus including a source lof fluid, a plurality of pumps, means dening a valve chamber in continuous communication with said pump means for receiving pressure fluid therefrom, a return passage means placing said valve chamber in communication with said source, and a pressure iluid confining space having a valve controlled outlet for working fluid and communicating with said valve chamber and With said source of fluid through inlet and relief passage means including check valves controlling the flow of fluid therethrough, and including a control valve in said chamber selectively positionable to connect one or more of said pumps with said inlet passage means and the remaining pumps, if any, with said return passage means, the combination of a relief and unloading means comprising a part associated with said relief passage means and movable in response to fluid pressure exerted thereon as a result of movement of the relief passage check valve to a position establishing a flow of fluid therepast, and means operably connecting said part with said control valve so that movement of the former results in movement of the latter to a position preventing the flow of fluid between one or more of said pumps and said working fluid passage.

3. In a hydraulic apparatus including' a pump means, means defining a valve chamber receiving pressure iiuid from said pump means, a iiuid return passage means communicating with said valve chamber, and a working fluid passage means communicating with said valve chamber and including check valves therein biased to establish a pressure iiuid confining space therebetween, and including a valve in said lchamber manually positionable to selectively connect said working and return passage means jointly and severally with the discharge side of said pump means, the combination of a pressure relief and unloading control comprising a relief passage means placing said pressure iiuid coniiining space in communication with said return passage means, and means controlling iiow of fluid through said relief passage means and including a part operatively connected with said valve, said means initially responding to attainment of a predetermined high pressure inrsai-d uid conning space to open said relief passage means and move said valve to a pump unloading position wherein less uid ows into said confining space, and then operating in response to a relatively low pressure in said conning space to maintain said relief passage means open for iioW of fluid therethrough and said valve in its said pump unloading position.

4. In a hydraulic apparatus including a pump means, means defining a valve chamber receiving pressure fluid from said pump means, a iiuid return passage means communicating with said valve chamber, and a working fluid passage means communicating with said valve chamber and including check valves therein operative to establish a pressure fluid conning space therebetween, and including a valve in said chamber manually positionable to selectively connect said working and return passage means jointly and severally with the discharge side of said pump means, the combination of a pressure relief and unloading control comprising a relief passage placing said pressure fluid confining space in communication with said return passage means, a flow control means for said relief passage including a rst portion of small area subjected to the pressure'in said iiuid confining spaceand a second portion of considerably larger area which is subjected to the pressure in said fluid confining space as a result of said first portion moving to its passage opening position, and additional means operatively connected with said valve to move same as a result of a movement of said iiow control means to its passage opening position, said flow control and additional means initially operating in response to attainment of a predetermined high pressure in said working fluid passage means to open said relief passage and move said valve to a pump means unloading position wherein less fluid iiows into said iiuid confining space, and then operating in response to a relatively low pressure in said working fluid passage means to maintain said relief passage means open for flow of fluid therethrough and said valve in its said pump means unloading position.

5. In a hydraulic apparatus including a plurality of pumps, means defining an intake pasconfining space in communication with said rev turn passage means, and including a control Valve in said housing positionable to selectively connect the discharge sides of said pumps with said working and return passage means or with either said working passage means or said return passage means, thecombination comprising vmeans controlling the flow of uid through said relief passage and including `a part operatively connected with said control valve, said means operating in response Ato attainment of a predetermined pressure in said pressure iiuid confining space to open said'relief passageiand' move Vsaid control valve to a position wherein one or more ofthe vpumps'is prevented from delivering fluid to said confining space.

6. A hydraulic' apparatus comprisinga source saidsource, a-manifoldspace, a pluralityof sepa-y rate passages, one foreach pump, connecting said valve chamber with saidmanifold space, a valve controlledV outlet toV said manifold space,r andv a second return passage'means placing said manifold spaceV in communication with'said source, a control valve in said chamber selectively positionable to connect one or more of said pumps withsaid separate passages and the remaining pumps with said rst return passage means, an additional control vfor said pumps including a movable element controlling they flow of fluid through said second return passage means and operative in response' to attainment of a prede- 'i termined pressure in said manifold space to openl said second return passage, and means operably connecting said movable element with said control valve so that a passage opening movement of said elementV results in a movement of said control valve to aposition wherein a fewer number of said pumps are delivering fluid to said pressure manifold.

7 In a hydraulic apparatus comprising a source of fluid, a plurality of pumps, means defining an intake passage placing said pumps in communication with said source, a valve chamber, pump outlet passages severally connecting said pumps with said valve' chamber, a uid return means connecting said Valve chamber with said source of fluid through a first group of passages conforming in number and generally related to said pumps, a manifold space communicating with said valve chamber through a second group of check valve 'controlled passages conforming in number and generally related to said pumps, a valve controlled outlet to said manifold space, and defining a relief passage means placing said manifold space in communication with said source, and comprising a control valve in said chamber positionable to selectively severally connect one or more of said pumps with one or more of said rst group of passages or with oneA or more of said second group of passages, the combination of a pressure relief and unloading control ncluding an element movable in response to attainment of a predetermined pressure in said manifold space to open said relief passage means for the flow of fluid therethrough, and including means connected with said control valve and operating as a result of a passage opening movement of said element to move said control valve to a position wherein one of said pumps continues delivering pressure iiuid to said manifold space and the remainder of said pumps are prevented from discharging fluid into said manifold space and deliver fluid to the related passages of said nrst group.

8. In a hydraulic apparatus comprising a source of fluid and parts constructed and combined to operatively house a plurality of pumps and denne an intake passage means placing said pumps in continuous communication with said source, a control valve chamber severally communicating with the discharge sides of said pumps, return passage means placing said control valve chamber in communication with said source of fluid, a pressure manifold communicating with said control valve chamber through passages each including a pressure maintaining valve therein, said passages conforming in number and being generally related to said pumps, a valve controlled outlet means for said pressure manifold, a control valve in said chamber selectively positionable to place all of said pumps in communication with said return passage means or to place one or more of said pumps in communication with its related passage leading to said pressure manifold, and comprising a relief passage means placing said pressure manifold in communication with said return passage means, the combination of a control for said relief passage means including an element movable in response to attainment of a predetermined pressure in said manifold to open said relief passage means for the flow of fluid therethrough, and means connecting said movable element with said control valve for effecting a pump unloading movement of the latter in response to a pressure produced movement of the former.

9. A hydraulic device comprising a housing operatively enclosing a pump means and including therein an intake passage means for said pump means, a valve chamber in communication with the discharge side of said pump means, a

uid return passage means in communication with said valve chamber, a manifold space, a rst passage means placing said manifold space in communication with said valve chamber, an outlet passage for said manifold space, said first passage means and outlet passage including valves controlling the admission and discharge of pressure fluid into and out of said space, respectively, a control valve in said chamber positionable to selectively connect the discharge side of said pump means with said first and return passage means or with either said first passage means or said return passage means, an additional control for said pump means comprising a second passage connecting said manifold space with said return passage means and an element controlling the flow of fluid through said second passage, said element moving to its passage opening position in response to attainment of a predetermined pressure in said manifold space, and means connected with said control valve and with a portion of said second passage in downstream relation with respect to said element, said last mentioned means including parts operative in response to the presence of pressure 16 iiuid in said second passage portion to move said control valve to a position wherein less fluid flows into said manifold space.

10. A hydraulic device comprising a housing operatively enclosing a pump means and including therein an intake passage means for said pump means, a valve chamber in communication with the discharge side of said pump means, a fluid return passage means in communication with said valve chamber, a manifold space, a first passage means placing said space in communication with said valve chamber, an outlet passage for said space, said first passage means and outlet passage including check valves biased to control the admission and discharge of pressure iiuid into and out of said space, respectively, a control valve in said chamber positionable to selectively connect the discharge side of said pump means with said rst and return passage means or with either said first passage means or said return passage means, an additional control for said pump means comprising a second passage connecting said manifold space with said return passage means land an element controlling the flow of fiuid through said second passage, said element moving to passage opening position in response to attainment of a predetermined pressure in said manifold space, and means operatively connecting said movable element with said control valve so that a passage opening movement of said element results in a movement oi said control valve to a position wherein less iiuid news into said manifold space.

ll. A hydraulic device comprising a housing operatively enclosing a pump means and including therein an intake passage means for said pump means, a valve chamber in communication with the discharge side of said pump means, a fluid return passage means in communication with said Valve chamber, a rst passage means communicating with said valve chamber, a control valve in said chamber positionaole to selectively connect the discharge side of said pump means with said rst and return passage means or with either said first passage means or said return passage means, said first passage means including check valves disposed in series flow relation therein and biased to control the admission and discharge of pressure fluid into and out of the space between said check valves, an additional control for said pump means comprising a second passage connecting said space with said return passage means and an element controlling the flow of fluid through said second passage, said element moving to passage opening position in response to attainment of a predetermined pressure in said space, and means connected with said control valve and with a portion of said second passage in downstream relation with respect to said element, said last mentioned means including parts operative in response to the presence of pressure uid in said second passage portion to move said control valve to a position wherein less fluid flows into said space between said check valves.

12. A hydraulic device comprising a housing operatively enclosing a pump means and including therein an intake passage means for said pump means, a valve chamber in communication with the discharge side of said pump means, a iiuid return passage means in communication with said valve chamber, a manifold space, a first passage means placing said manifold space in communication with said valve chamber, an outlet passage for said manifold space, said first f passage means and outlet passage including check valves therein, a control valve in said chamber positionable to selectively connect the discharge side of said pump means with said first and returnpassage means or with either said first passage means or said return passage means, an additional control for said pump means comprising a second passage connecting said manifold spacewith said return passage means, and means controlling the flow of iiuid through said second passage and including a part operatively connected with said control valve, said means operating in response to attainment of a lpredetermined pressure in said manifold space to open "said second passage and move saidV control valve toa position wherein less iiuid flows into said manifold space. v

13. In a hydraulic apparatus including a pump means, means defining an intake passage for said pump means, a valve housing in communication with the discharge side of said pump means, and defining va fluid return passage means `in communication with said Vvalve housing, a hydraulic motor communicating with said valve housing through a working fluid conflning passage means; for relieving fluid pressure on said motor comprising passage means including a portion of said valve housing, and including a valve in said housing positionable to selectively connect the discharge side of said pump means with said working iiuid and return passage means or with either 'said' working fluid passage means or with said return passage means, said valve, when moved to a position wherein all fluid discharged fromsaid pump means is delivered to said return passage means, being further movable toalso place said motor relieving passage means in communication with said' return passage means, and a further control for said pump means operative when said valve is positioned so as to attain a high pressure 'operating in response to attainment of a predetermined pressure in said working iiuid passage means to open said relief passage and move said valve to a position wherein less fluid iiows into saidlworking fluid passage means, and also operating in response to a failure of pressure in said working fluid passage means to effect a return of said valve to vits initial high 'pressure attaining position. u l

' 14. A hydraulic lcontrol device comprising a housing having a main inlet passage adapted for communication with a source of liquid,ra plurality of pumps within said housing, said housing including inlet passages severally connecting said pumps with said main passage, a cylindrical valve chamber, a first group of passages severally connecting the discharge sides of said pumpswith said valve chamber, a return passage meansv communicating with said source, a second group of passages placing said valve chamber in communication with said return passage means and conforming in number and generally related to said pumps, a pressure iiuid confining space having a check valve controlled outlet, said space being infcomrnunication Ywith said valve chamberthrougha'third' group ofrcheck valve controlled passages conforming innumber andgen- 'cylindrical' control valve in said valve chamber through related ones of said third group of passages and the remaining pumps, if any, with said return Vpassage means through related ones of said second group of passages, a separate means for relieving the pressure head on one or more of said pumps comprising an auxiliary passagey placing said pressure fluid confining space in communication with said return passage means vand an element controlling the flow of fluid through said auxiliary passage, said element being movable to open said auxiliary passage in response to attainment of a predetermined pressure( in said manifold, and linkage means operablyk connecting said movable element with said control valve so that a passage opening movement ofsaid element results in a movement of said control valve to a position wherein a fewer number of said pumps are delivering fluid to said pressure conlining space.

15. A hydraulic apparatus comprising a -housing having a main inlet passage adapted for communication with a source of fluid, a plurality`v of pumps within said housing, said housing including inlet passages severally connecting said pumps with said main passage, a cylindrical valve chamber, a first group of passages severally connecting the discharge sides of said pumpsV with saidfvalve chamber, a bypass duct in said housing arranged to return fluid to said source, a second group of passages placing said valve chamber in communication with said bypass duct and conforming 'in number and generally related to said pumps, and a pressure iiuid confining space having a check valve controlled outlet, said space being incommunication with saidvalve chamber througlia third group of check valve controlled passages conforming in number and `generally relatedto said pumps, a hydraulic motor connected'with said check valve controlled' outlet, means for relieving fluid pressure on said motor comprising passage means including a portion of said valve chamber, an annular groovedcylindrical control valve in said valve chamber selectively positionable to selectively severally connectone or more of said pumps with said bypass duct throughsaid second group vof passages and the remaining pumps, if any. with said pressure fluid confining space through said third group of passages, said said iiuid confining space, said assembly mov- Y ing in response to attainment of a predetermined pressure in said fluid confining space to place portions of said unloading valve chamber on opposite sides of said assembly in communication with said iiuid confining space, a spring biased piston disposed in said unloading valve chamber in spaced relation to said assembly and movable in response to pressure fluid entering the space therebetweenA and means loperably connecting said spring biased piston with said control valve 'so thatmovement ofthe formerresults in.Y movement of the latter to' a position wherein only one of said pumps is delivering fluid to-saidfluid confining space.

16. In a hydraulic apparatus including a source of' fluid, a plurality of pumps, means defining intake passages adapted to connect said pumps with said source of duid, pump outlet passages, a valve chamber communicating with said outlet passages, a return passage means connected with said valve chamber and adapted to conduct fluid to saidv source, and a working fluid passage means communicating with said valve chamber and including valves operative to establish a'pressure fluidV confining space therebetween, andincluding a control Valve in said incommunication with said return passage d means, an additional control comprising means defining a pressure relief passage communicating with said fluid confining space, and an unloading chamber communicating with said relief passage and with said return passage means, a check' valve and piston assembly disposed in said unloading chamber and controlling communication with said fluid confining space, said assembly moving in response to attainment of a predetermined pressure in said fluid confining space to place portions of said chamber on opposite sides of Vsaid assembly in communication with said space, a spring'biased piston disposed in said chamber in spaced vrelation to said assembly and movable in response to pressure fluid entering the space therebetween, said biased piston controlling communication between said unloading chamber and said return passage means, and means. operably connecting said spring biased piston with said control Valve so that movement of the, former results in movement of the latter to a position wherein only one of said pumps delivering fluid' to said fluid confining'space and the remaining pumps are delivering' fluid to said return passage means.

1.7. In a hydraulic apparatus including a source of fluid, a plurality of pumps, means defining a valvev chamber receiving pressure fluid from said pumps, a return passage means placing said valve chember in communication with said source, and a. first passage means communicating with said valve chamber and including valves establishing a pressure confining space therebetween, and including a control valve in said valve chamber selectively positionable to connect' one or more of said pumps with said first passage means and the remaining pumps, if any, with said return passage means, the combination of a relief and unloading means comprising a relief passage placing said fluid confining space in communication with said source, a first part controlling the flow of fluid through said relief passage and movable in response to an excess of pressure in said fluid confining space, a second part disposed in flow-controlling down-stream relation with respect to said first part and movable in response to fluid pressure exerted thereon as a result of a movement of said first part to a position establishing a flow of fluid therepast, and a linkage operatively connecting said second'part with said control valve so that movement of said second part results in a movement of said control valve to a position wherein the fluid discharged from one or more of said pumps is prevented from flowing into said fluid confining space and flows'` 20 through said returnV passage meansl andbaclc. to

said source.

18. In a hydraulic apparatus havingv a source of liquid, a plurality of pump in communication with said'source, a pressure fluid confining; space. a fluid return passage means, and having afvalve selectively positionable to connect oneE or more of said pumps with said pressure fluid confining space and the remaining pumps, if any, with said return passage means, the combination of a relief and unloading means comprising an unloading chamber communicating with said fluid conlining space and with said retum passage means, a check valve and piston assembly disposed in said unloading chamber andfcontrolling'the flow of fluidr therethrough, said assembly moving in response to attainment of a predetermined pressure in said fluid confining space to place portions of said chamber on opposite sides of said assembly in communication with said space, a spring-biased piston disposed in said. chamber in spacedk relation to said assembly and movable in response to pressure fluid entering the space therebetween, and means operably connecting said spring: biased piston with said control valve so that move-ment of the former results in movement of the latter to a, position wherein only one of said pumps is delivering fluid to saidpressure manifold. Y

19. In a hydraulic apparatus having a source of liquid, a plurality of pumps in communication with said source, a pressure fluid confining space, a fluid return passage means, and having 'a valve selectively positionable to connect one or more of said pumps with said pressure fluid confining space and the remaining pumps, if any, with said return passage means, the combination of a relief and unloading means comprising an unloading chamber communicating with said fluid conning space, a first part of said chamber including therein a check valve and piston assembly operative to move to a position fo-rflow of fluid therepast in response to attainment of a predetermined pressure in said fluid confining space. a second `part of said chamber communicating with said first part and with said return passage means, a spring biased piston disposed in said second part and movable in response to fluid pressure exerted thereon as a result of movement of said assembly to a position establishing a flow of fluid therepast, and means operably connecting said spring biased piston with said control valve so that movement of the former results in movement of the latter to a position wherein only one of said pumps is delivering fluid to said fluid conning space.

20. In a hydraulic apparatus having a source of liquid, a plurality of pumps in communication with said source, a pressure fluid confining space, a fluid return passage means, and having a valve selectively positionable to connect one or more of said pumps with said pressure fluid confining space and the remaining pumps, if any, with said return passage means, the combination of a relief and unloading means comprising an unloading valve chamber communicating with said pressure manifold and said return passage means, a check valve and piston assembly disposed in a first portion of said chamber and controlling the flow of fluid from said manifold to said source and movable in response to an excess of pressure in said manifoldl a spring biased piston disposed in a second portion of said chamber in spaced relation to said assembly and controlling communicaton, between said unloading ammira 2-1l valve chamber-and said! -returnpassage means, said piston being movable-in-response to fluid pressure exerted thereon as a result of a movement of said first part to a position establishing a flow of liquidtherepast, andalinkage operatively connecting said spring biased pistonA with said control valve so that movement of said piston vresults 4in-,a movement of said controlv'alve ,to

aipositionwherein thefluid discharged `fronfo'ne or more' of said pumpsis prevented fromf'flowing into said fluid confining space and flows through said return passage means and back to said source.

21. In a hydraulic apparatus including a pump means, means defining an intake passage for said pump means, a valve housing in communication with the discharge side of said pump means, a fluid return passage means in communication with said valve housing, a pressure maintaining working fluid passage means communicating with said valve housing, and defining a pressure relief passage means placing said working fluid passage means in communication with said return passage means, and including a valve in said housing positionable to selectively connect the discharge side of said pump means with said Working and return passage means or with either said Working fluid passage means or said return passage means, the combination comprising additional means controlling the flow of fluid through said relief passage means and including a part operatively connected with said control valve, said means operating in responsev to attainment of a predetermined pressure in said working fluid passage means to open said relief passage means and move said control valve to a position wherein I ,l

less fluid flows into said working fluid passage means.

means, means defining an intake passage for said pump means, a valve housing in communication with the discharge side of said pump means, a working fluid confining passage means, and defining a fluid return passage means in communication with said valve housing, a hydraulic motor communicating with said valve housing through said working fluid confining passage means, and including a valve in said housing positionable to selectively connect the discharge side of said pump means with said working fluid and return passage means or with said working fluid passage means so as to-attain a high pressure in said working fluid passage means, the combination comprising means defining a relief passage placing said working fluid passage means in communication with said return passage means, and an additional means controlling the flow of fluid through said relief passage and operatively connected with said valve, said additional means operating in response to attainment of a predetermined pressure in said working fluid passage means to open said relief passage and move said valve to a position wherein less fluid flows into said working fluid passage means.

23. In a hydraulic apparatus including a pump means, means defining a valve chamber receiving pressure fluid from said pump means, a fluid return passage means communicating with said valve chamber, and a working fluid passage means communicating with said valve chamber,

check valves operatively associated with said working fluid passage means so as to maintain the working fluid confined therein at a pressure less than a predetermined value, and including nected with said valve-,'s`aid means `operating 'a --vaive Ain' said `chamber manuallygpsitionabre tol selectively connect lsaidl' workingandf turn sage means and including a par'toperativel m response to attainment 4of said predetermined value of working fluid pressure to open saidrelief passage and move said valveyto a position wherein less uidis delivered to--s'aid working fluid passage means.

24. In a hydraulic apparatus including a pump means, means defining an intake passage for said pump means, a valve housing in communication with the discharge side of said pump means, a working fluid confining passage means, and defining a fluid return passage means in communication with said valve housing, a hydraulic motor communicating with said valve housing through said working fluid confining passage means, and including a valve in said housing positionable to selectively connect the discharge side of said pump means with said working fluid and return passage means or with said working fluid passage means so as to attain a high pressure in said working fluid passage means, the combination comprising means defining a relief passage placing said working fluid passage means in communication with said return passage means, and additional means controlling the flow of fluid through said relief passage and operatively connected with said valve, said additional means initially operating in response to attainment of a predetermined high pressure in said working fluid passage means to open said relief passage and move said valve to a position wherein less fluid-flows into said working fluid passage means, and then operating in response to a relatively low pressure in said working fluid passage means to maintain said relief passage open for flow of fluid therethrough and said valve in its said position wherein less fluid flows into said working fluid passage means.

2-5. In a hydraulic apparatus including a pump means, means defining an intake passage for said pump means, a valve housing in communication with the discharge side of said pump means, and defining a fluid return passage means in communication with said valve housing, a hydraulic motor communicating with said valve housing through a working fluid confining passage means, and including a valve in said housing positionable to selectively connect the discharge side of said pump means with said working fluid and return passage means or with said working fluid passage means so as to attain a high pressure in said working fluid passage means, and a further control for said pump means comprising means defining a relief passage placing said working fluid passage means in communication with said return passage means, a flow control means for said relief passage including a first portion of small area subjected to the pressure in said working fluid passage means and a second portion of considerably larger area which is subjected to the pressure in said working fluid passage means as a result of said first portion moving to its passage opening position, and additional means operatively connected with said valve to move same as a result of a movement .fluid passage means to open said relief passage and move said valve to a pump means unloading posi-tion wherein less fluid-ows into said working Huid passage means, and then operating in response to a relatively low pressure in said working uid passage means to maintain said relief passage means open for ow of fluid therethrough and said valve in its said unloading position.

IGOR KAMLUKIN.

24 REFERENCES CITED The 'following references are of record .in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,002,306 Perkins Sept. r5, 1911 1,770,297 Bussmann July 8, 1930 1,888,542V Rosberg Nov. 22, 1932 2,247,261 Towler et al June 24, 1941 

